The milbemycins form an important group of broad spectrum antiparasitic agents possessing anthelmintic, ectoparasiticidal, insecticidal, antibacterial, antifungal and growth promoting activity with application in the areas of animal and human health, agriculture and horticulture. They are produced by fermentation of certain microorganisms of the genus Streptomyces under aerobic conditions in an aqueous or solid nutrient medium containing inorganic salts and assimilable sources of carbon and nitrogen. For example, fermentation of the microorganism Streptomyces hygroscopicus spp aureolacrimosus B-41-146 as described in British patent specification 1390336 produces a family of milbemycins known collectively as the B-41 compounds. In another example, fermentation of Streptomyces cyaneogriseus spp noncyanogenus as described in European patent specification EP-A-0170006 produces another family of milbemycins known collectively as the LL-F28249 compounds.
Compounds related to the milbemycins are described in EP-A-0254583. They are obtained by fermentation of Streptomyces micro-organisms known as Streptomyces E225 and Streptomyces E225B.